Unleaded solder alloy and electronic components using it

ABSTRACT

Wire burst faults at the time of solder attachment of conductors of an electronic component using insulation coated conductors having a core of copper or alloy containing alloy, is prevented.  
     Solder attachment of connecting portions of insulation coated conductors having copper as a base material is carried out by melting lead-free solder alloy containing from 5.3 to 7.0 wt % copper (Cu), from 0.1 to less than 0.5 wt % nickel (Ni), with a remainder being tin (Sn), at a temperature ranging from 400° C. to 480° C.

TECHNICAL FIELD

[0001] The present invention relates to a solder alloy that does notcontain lead, namely lead-free solder alloy, and particularly to anelectronic component using this lead-free solder alloy.

BACKGROUND ART

[0002] In the related art, tin (Sn)-lead (Pb) type solder alloy hasoften been used as solder for electrical connections within anelectronic component or for connecting electronic components to aprinted circuit boad.

[0003] In recent years, the toxicity of lead has been seen as a problem,and the legal restriction of use of lead has been investigated. For thisreason, the development of solder alloy having an extremely low leadcontent, or lead-free solder alloy having no lead content whatsoever toreplace Sn—Pb type solder alloy has been hastened.

[0004] As an example of a lead-free solder alloy, there are thedisclosures in Japanese Patent No. 3036636, and U.S. Pat. No. 4,758,407.

[0005] Japanese Patent No. 3036636 relates to a lead-free solder alloyfor bonding electronic components to a printed circuit boad of anelectronic device, and has part of a copper component of tin(Sn)-copper(Cu) alloy replaced by nickel (Ni) with the compositional ratio beingCu: 0.05-2.0 weight %, Ni: 0.001-2.0 weight % and the remainder beingSn. The purpose of this is to increase mechanical strength of thebonding sections.

[0006] Also, U.S. Pat. No. 4,758,407 proposes use of copper pipe andbrass pipe as mains water pipe, in order to prevent lead and cadmiumleaking into drinking water from lead pipes used in mains water pipes,and the invention of this patent relates to a solder alloy for weldingthese copper pipes and brass pipes to connecting joints in order to jointhem together for extension purposes.

[0007] The main component of this solder alloy is tin(Sn) or tin (Sn)and Antimony (Sb), and neither solder contains lead (Pb) or cadmium(Cd). Here, the composition of the solder alloy having tin as a maincomponent is Sn: 92.5-96.9 wt %, Cu:3.0-5.0 wt %, Ni: 0.1-0 2.0 wt %,Ag: 0.0-5.0 wt %.

[0008] Also, the composition of the solder alloy having tin/antimony asa main component is Sn: 87.0-92.9 wt %, Sb: 4.0-6.0 wt %, Cu: 3.0-5.0 wt%, Ni: 0.0-2.0 wt %, Ag: 0.0-5.0 wt %.

[0009] The melting temperature of the solder alloy of Japanese PatentNo. 3036636 is around 230° C., and this solder alloy, as mentionedabove, is for bonding electronic components to conductive portions of aprinted circuit boad , which means that the melting temperature(temperature at the time of reflow) is preferably as low as possible.

[0010] Also, the melting temperature of the solder alloy of U.S. Pat.No. 4,758,407 is from around 240° C. to around 330° C., but this solderalloy is used for welding together copper pipe or brass pipe or theirjoints used as water supply pipes in, for example, a domestic waterheater, which means that when considering operability at the time ofmelting, the melting temperature of this alloy solder is preferably low.

[0011] Inside the electronic components there are high frequency coilsor transformers formed by winding linear or substantially belt-shapedelectrical conductors (referred to below as windings). Wires that havean insulating coat formed by coating a copper core with enamel orurethane are used as these coil windings.

[0012] With the coils, it is necessary to attach solder in order toelectrically connect each of the two ends of the winding wound on abobbin etc., namely a starting end and a finishing end, to electrodessuch as terminal pins provided on the bottom of the bobbin.

[0013] In order to attach the solder to the terminals and carry outelectrical connection, it is necessary to remove the insulating coatfrom the tip of the wire. Generally, as a method of removing theinsulating coat, there is a method of mechanically scraping off thecoat, a method of dissolving the coat using chemicals, and a method ofdecomposing or dissolving the coat using high temperature heating.

[0014] It has been common practice in the related art to adopt themethod using high temperature heating.

[0015] For example, in order to manufacture a coil, each of a startingend and a finishing end of a winding are wrapped around electrodesections such as terminal pins provided in the bottom of a bobbin etc.,followed by dipping the wrapped sections into solder liquid that hasbeen heated to a high temperature. Specifically, a method is generallyused where the insulating coat of the windings is removed simultaneouslywith attaching the solder.

[0016] At the time of solder attachment, when using lead-free solderthat does not contain a copper component, while the tip of the electrodeis being brought into contact with the molten solder (solder liquid), aphenomenon known as “copper erosion” arises where copper that is thebase material is dissolved in the solder liquid and made thinner. Thiscopper erosion phenomenon is a major factor causing wire bursts inelectronic components such as the above described coil.

[0017] With this phenomenon, the amount of copper dissolved in thesolder liquid increases as the melting temperature of the solderincreases, and the rate of copper dissolving also increases withincreased melting temperature. Accordingly, it is easy for the abovedescribed open-circuit problems to occur if the diameter of anelectrical wire tapers off. On the other hand, in order to prevent thecopper erosion phenomenon, means for attaching microscopic amounts ofcopper to the lead-free solder alloy is generally known. However, if thecopper content becomes excessive, the viscosity of the molten solder(solder liquid) increases, and a phenomena where more solder than isnecessary becomes attached to sites to which solder is to be attached sothat solder hangs down in the shape of icicles, causing a bridgephenomenon where excess solder straddles across adjacent sites. Besidesthis, if the copper content becomes excessive, there are problems suchas the plating weight (weight of attached solder) becoming non-uniform,and wetting becoming poor.

[0018] Also, if the melting temperature of the molten solder is low, aninsulating coat material of enamel or urethane is not completelydissolved, which is the main cause of incomplete solder attachment andpoor continuity etc. The melting temperature of the lead-free solderalloy tends to increase with increase in the copper content.

DISCLOSURE OF THE INVENTION

[0019] A first aspect of the present invention provides a lead-freesolder alloy containing from 5.3 to 7.0 wt % copper (Cu), from 0.1 toless than 0.5 wt % nickel, and the remainder being tin (Sn). A secondaspect of the present invention provides an electronic component, havinga core formed from copper or an alloy containing copper that usesconductors having the cores coated with an insulating coat, theconductors, or the conductors and sites other than the electroniccomponent provided with solder using a lead free solder alloy containingthe above described 5.3 to 7.0 wt % copper (Cu) from 0.1 to less than0.5 wt % nickel (Ni) and the remainder being tin (Sn), and in this way,open circuit faults caused by the copper erosion phenomenon of the abovedescribed electronic component are prevented.

[0020] A third aspect of the present invention is basically the same asthe second aspect of the invention, wherein at the time of attachingsolder to the electronic component, the insulating coat of theconductors is reliably dissolved by setting the melting temperature ofthe lead-free solder to from 400° C. to 480° C.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is an explanatory drawing showing one example of a coilcomponent.

PREFERRED MODE OF EMBODYING THE INVENTION

[0022] As described previously, inside the electronic components thereare high frequency coils or transformers (hereafter referred to ascoils) formed by winding linear. or substantially belt-shaped electricalconductors (referred to below as windings). Wires that have aninsulating film formed by coating a copper core with enamel or urethaneare used as these coil windings. One example of a coil using wires thathave an insulating film formed by coating a copper core with enamel orurethane as the coil windings is shown in FIG. 1.

[0023] In FIG. 1, reference numeral 1 is a coil, 2 is a bobbin, and inthis embodiment they are integrally formed from ferrite core. Referencenumeral 3 is winding material formed by coating a copper core with aninsulating coat of enamel or urethane, 4 is a winding section having thewinding material 3 wound around a body section of the bobbin 2, 5 is aterminal pin embedded in the bottom of the bobbin 2, 6, 6 are thestarting end and finishing end lead out terminal of the winding materialand electrically connected to the terminal pin 5 by being wrappedaround.

[0024] The terminal pin 5 is for electrically connecting the coil 1 tocircuit conductors of a circuit substrate (not shown). An HCP wirehaving copper plating coated on the surface of a steel wire is commonlyused as the terminal pin 5.

[0025] Here, in order to electrically connect the wiring section 4 andthe terminal pin 5, it is necessary to remove the insulating coat of atip end of a lead out terminal 6 constituting a wrapping section 7. Asmentioned above, as a method of removing the insulating coat of thewinding material 3, there is a method of mechanically scraping off thecoat, a method of dissolving the coat using chemicals, and a method ofdecomposing or dissolving the coat using high temperature heating, butin the present invention the high temperature heating method is adopted.

[0026] Specifically, after wrapping the lead out terminal 6 of thewinding section wound around the body section of the bobbin 2, coatingmaterial of the insulation coated conductors is removed by the heat ofthe liquid solder by dipping the wrapping section into a solder bath.

[0027] The inventor carried out experiments with coils using lead-freesolder having copper added to tin, and it was not possible to completelyremove enamel coating with a solder attachment temperature of less than350° C.

Practical Example

[0028] Table 1 contains measurement results showing a relationshipbetween solder attachment temperature when enamel coated copper wirehaving a diameter of 0.4 mm is dipped in a molten solder liquid, andshows a relationship between the compositional content of the solderalloy and solder attachment temperature, extent of copper erosion, andthe condition of the solder attachment surface.

[0029] In table 1, “extent of copper erosion” has the conductor diameterof the enamel coated copper wire before solder attachment (0.4 mm) as areference, with a reduction of 10% being “large”, a reduction of from 5%to less than 10% being “medium”, and a reduction of from 0 to less than5% being “small”.

[0030] Also, “enlarged” means that it was possible to increase thediameter of the copper wire compared to the reference value. TABLE 1diameter of 0.4 mm enamel Solder coated Composition (Cu: Solder copperwire condition of 4.0-8.0 wt %, attachment after solder extent of solderNi: 0.0-0.6 wt %, temperature attachment copper attachment Sn:remainder) (° C.). (mm) erosion surface Sn-4Cu 480 0.302 large Sn-5.3Cu480 0.343 large non-uniform thickness Sn-6Cu 480 0.349 large Sn-7Cu 4800.360 large Sn-8Cu 480 0.365 medium Sn-4Cu 450 0.345 large Sn-5.3Cu 4500.356 large Sn-6Cu 450 0.370 medium Sn-7Cu 450 0.391 small thicknessnon-uniform Sn-8Cu 450 0.408 slightly icicle  enlarged Sn-4Cu 400 0.365medium Sn-5.3Cu 400 0.370 medium Sn-6Cu 400 0.380 medium Sn-7Cu 4000.409 slightly icicles enlarged Sn-8Cu 400 0.417 enlarged iciclesSn-4Cu-0.2Ni 480 0.320 large Sn-5.3Cu-0.1Ni 480 0.352 largeSn-5.3Cu-0.2Ni 480 0.359 large Sn-5.3Cu-0.5Ni 480 0.372 mediumSn-5.3Cu-0.6Ni 480 0.374 medium Sn-6Cu-0.1Ni 480 0.386 smallSn-6Cu-0.2Ni 480 0.382 small Sn-6Cu-0.5Ni 480 0.389 small Sn-6Cu-0.6Ni480 0.395 small Sn-7Cu-0.1Ni 480 0.382 small Sn-7Cu-0.2Ni 480 0.378medium Sn-7Cu-0.5Ni 480 0.395 small Sn-7Cu-0.6Ni 480 0.411 enlargedSn-8Cu-0.6Ni 480 0.418 enlarged Sn-5.3Cu-0.1Ni 450 0.378 mediumSn-5.3Cu-0.2Ni 450 0.379 medium Sn-5.3Cu-0.5Ni 450 0.383 smallSn-5.3Cu-0.6Ni 450 0.381 small Sn-6Cu-0.1Ni 450 0.382 mediumSn-6Cu-0.2Ni 450 0.385 small Sn-6Cu-0.5Ni 450 0.392 small Sn-6Cu-0.6Ni450 0.399 small Sn-7Cu-0.1Ni 450 0.380 small Sn-7Cu-0.2Ni 450 0.387small Sn-7Cu-0.5Ni 450 0.395 small Sn-7Cu-0.6Ni 450 0.410 enlargedicicles Sn-5.3Cu-0.1Ni 400 0.378 medium Sn-5.3Cu-0.2Ni 400 0.384 smallSn-5.3Cu-0.5Ni 400 0.387 small Sn-5.3Cu-0.6Ni 400 0.387 smallSn-6Cu-0.1Ni 400 0.392 small Sn-6Cu-0.2Ni 400 0.389 small Sn-6Cu-0.5Ni400 0.390 small Sn-6Cu-0.6Ni 400 0.410 enlarged Sn-7Cu-0.1Ni 400 0.381small Sn-7Cu-0.2Ni 400 0.392 small Sn-7Cu-0.5Ni 400 0.405 smallSn-7Cu-0.6Ni 400 0.418 enlarged icicles Sn-8Cu-0.6Ni 400 0.423 enlargedThickness non-uniform

[0031] As is clear from the practical examples of table 1 above, withsolder alloy of tin-copper only, the extent of copper erosion increaseswith decrease in the copper content, for example, in the case of acopper content of 4 wt % and the remainder tin, the diameter of theenamel coated copper wire was reduced by 24.5%.

[0032] Also, if the copper content is increased with solder alloy oftin-copper only, the viscosity of the molten solder increases in theregions where the solder melting temperature is low, causing a platingthickness of the solder attachment sections to become non-uniform,diameter of the enamel coated conductors is enlarged compared to thereference value, and a phenomenon arises where excessive solder hangsdown.

[0033] Further, with Sn-7Cu solder alloy with 7 wt % Cu added to thetin, and Sn-8 Cu alloy solder with 8 wt % Cu added to tin, when themelting temperature is 400° C., an icicle phenomenon arises. On thecontrary, with solder alloy having 5.3 wt % Cu and 0.2 wt % nickel addedto the tin (Sn-5.3Cu-0.2Ni), the diameter of the enamel coated wire isonly reduced by 4% from the reference value, it is possible to make thecopper erosion extent extremely small, and wetting is also improved. Itis also possible to increase the mechanical strength of the solderattachment sections.

[0034] If the added amount of nickel exceeds a specified range in aregion where the copper content exceeds a specified amount, acopper-nickel precipitate floats in the molten solder, and since theprecipitate adheres to the surface of the solder attachment regions, thesolder attachment surface becomes microscopically uneven and ravaged,the thickness of the solder is not uniform, it is more likely that abridge phenomenon or icicle phenomenon will occur, and wettingdeteriorates. It was confirmed that it was easier for these phenomena tooccur in a region where the melting temperature of the solder alloy islow.

[0035] Next, the number of times solder is attached until the surfaceluster blackens, when repeatedly attaching solder to a HCP wire of 0.7mm diameter (manufactured by Fuji Electric wire Company) is shown intable 2. TABLE 2 number of times until terminal surface luster solderblackens when solder attachment repeatedly icicles compositiontemperature (° C.) attaching solder generated Sn-4Cu 480 3 no Sn-5.3Cu480 3 no Sn-6Cu 480 4 no Sn-7Cu 480 5 no Sn-8Cu 480 6 no Sn-5.3Cu 450 5no Sn-6Cu 450 6 no Sn-7Cu 450 9 no Sn-8Cu 450 14 no Sn-4Cu 400 4 noSn-5.3Cu 400 5 no Sn-6Cu 400 5 no Sn-7Cu 400 17 no Sn-8Cu 400 20 or moreyes Sn-4Cu-0.1Ni 480 4 no Sn-4Cu-0.2Ni 480 3 no Sn-5.3Cu-0.1Ni 480 3 noSn-5.3Cu-0.2Ni 480 5 no Sn-5.3Cu-0.5Ni 480 7 no Sn-5.3Cu-0.6Ni 480 7 noSn-6Cu-0.1Ni 480 7 no Sn-6Cu-0.2Ni 480 9 no Sn-7Cu-0.1Ni 480 8 noSn-7Cu-0.2Ni 480 9 no Sn-7Cu-0.5Ni 480 10 no Sn-7Cu-0.6Ni 480 10 noSn-8Cu-0.6Ni 480 15 or more no Sn-5.3Cu-0.1Ni 450 6 no Sn-5.3Cu-0.2Ni450 7-20 no Sn-6Cu-0.1Ni 450 13 no Sn-6Cu-0.2Ni 450 20 or more noSn-7Cu-0.1Ni 450 20 or more no Sn-7Cu-0.2Ni 450 20 or more noSn-5.3Cu-0.1Ni 400 20 or more no Sn-5.3Cu-0.2Ni 400 20 or more noSn-6Cu-0.1Ni 400 20 or more no Sn-6Cu-0.2Ni 400 20 or more noSn-7Cu-0.1Ni 400 20 or more no Sn-7Cu-0.2Ni 400 20 or more noSn-7Cu-0.5Ni 400 20 or more no Sn-7Cu-0.6Ni 400 20 or more yesSn-8Cu-0.6Ni 400 20 or more yes

[0036] As has been described above, the HCP wire is copper platingcoated on a surface of a steel wire, and is used as a terminal pin 5 ofthe coil of FIG. 1 or as terminal conductors of other electroniccomponents.

[0037] Table 2 shows the relationship between the number of times untilthe copper plate of the HCP wire is peeled away from the steel wiresection, which is the undercoat, and the composition of the solder alloyand the temperature at the time of solder attachment, and shows that asthe number of times increases, the degree of peeling of the copper platedecreases, in other words, the rate of copper erosion and the amount ofcopper erosion is reduced.

[0038] In particular, it will be understood that in the cases where amoderate amount of nickel has been added, it is unlikely that coppererosion will occur even in a region where the solder attachmenttemperature is high.

Industrial Applicability

[0039] The lead-free solder alloy of the present invention, as has beendescribed above, is not prone to copper erosion even in a region wheresolder attachment temperature is high, and it is possible to reduce theamount of copper lost due to the copper erosion.

[0040] Accordingly, it is possible to prevent wire burst at the time ofattaching solder to an electronic component that uses insulation coatedon a copper wire or alloy wire containing copper, and this effect isparticularly noticeable with insulation coated conductors of finediameter.

[0041] Also, since it is possible to reliably dissolve the insulatingcoating material of the insulation coated conductors using hightemperature solder attachment, it is possible to prevent bad continuitydue to residual insulating coating material.

1. Lead-free solder alloy containing from 5.3 to 7.0 wt % copper (Cu),from 0.1 to less than 0.5 wt % nickel (Ni), with a remainder being tin(Sn).
 2. An electronic component using conductors having a wire formedwith copper or an alloy containing copper, the wire being coated with aninsulating coating, wherein associated conductors, or the conductors andother sites on the electronic component, are subjected to solderattachment using a lead-free solder alloy containing from 5.3 to 7.0 wt% copper (Cu), from 0.1 to less than 0.5 wt % nickel (Ni), with aremainder being tin (Sn).
 3. An electronic component that is subjectedto solder attachment by melting lead-free solder alloy containing from5.3 to 7.0 wt % copper (Cu), from 0.1 to less than 0.5 wt % nickel (Ni),with a remainder being tin (Sn), at a temperature of from 400° C. to480° C.